[Utilization of rubidium 86 for humoral cytotoxicity tracing of sarcoma 180]

86Rb has been used as a tracer for Sarcoma 180 ascitic cells in a humoral cytotoxicity system, and compared with the trypan blue dye exclusion method. In as little as five minutes after contact with antiserum and complement, about 90 p. cent of the isotope has gone from the cells, with a significant difference between controls and experimentals. There is a good correlation between 86Rb and trypan blue dye exclusion results. The only pitfall is a relative fragility of cells during the centrifugation stages of the two washings.